fix: correct TOC links and vscode tasks for adding agents and prompts in CONTRIBUTING.md

[rs38]

This pull request introduces a new "Terminal Helper" agent for PowerShell and Bash, updates documentation to reference and describe this agent, and makes minor improvements to task naming and documentation consistency.

New Agent Addition:

• Added the terminal-helper agent, a concise terminal syntax and command helper for PowerShell and Bash, including its agent definition and behavioral guidelines (agents/terminal-helper.agent.md).

Documentation Updates:

• Registered the new "Terminal Helper" agent in the agents documentation table, including install links and a short description (docs/README.agents.md).
• Updated the contributing guide to clarify the section about adding agents, improving section naming consistency (CONTRIBUTING.md).

Build and Validation Workflow:

• Renamed the validate-collections VS Code task to validate-plugins and updated its command and description to match its purpose (.vscode/tasks.json).

Summary

• Changed the section title from "Adding Agents" to "Adding an Agent" for clarity in the contribution instructions.
• removing outdated TOC prompts-link
• fixed vscode tasks broken since Deprecate Collections in favour of Plugins #717
• added a terminal helper Agent

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, or workflow file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, or workflow with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the staged branch for this pull request.

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Type of Contribution

• New agent file.
• Other (please specify): TOC fix and vscode task

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull request overview

Updates the contribution guidelines Table of Contents to fix navigation for the “Adding an Agent” section and remove an outdated TOC entry for prompts.

Changes:

• Removed the “Adding Prompts” TOC entry (no corresponding section exists).
• Updated the “Adding Agents” TOC link target to point to #adding-an-agent.

[github-actions]

🔍 Skill Validator Results

✅ All checks passed

Scope	Checked
Skills	1
Agents	1
Total	2
Severity	Count
---	---:
❌ Errors	0
⚠️ Warnings	0
ℹ️ Advisories	0

Summary

Level	Finding
ℹ️	Found 1 agent(s)
ℹ️	Validated 1 agent(s)
ℹ️	✅ All checks passed (1 agent(s))

Full validator output

```text Found 1 agent(s) Validated 1 agent(s)

✅ All checks passed (1 agent(s))

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